Application Diagram
Once the value of PD(max) is known, the maximum permis-
Heat Sinks
sible value of RQJA can be calculated:
Each material in the heat flow path between the IC and
the outside environment will have a thermal resistance.
Like series electrical resistances, these resistances are
150¡C - TA
(2)
RQJA
=
PD
summed to determine the value of RQJA
:
The value of RQJA can then be compared with those in
R
QJA = RQJC + RQCS + RQSA
(3)
the package section of the data sheet. Those packages with
where:
R
QJA's less than the calculated value in equation 2 will
R
R
R
QJC = the junctionÐtoÐcase thermal resistance,
QCS = the caseÐtoÐheatsink thermal resistance, and
QSA = the heatsinkÐtoÐambient thermal resistance.
QJC appears in the package section of the data sheet. Like
QJA, it too is a function of package type. RQCS and RQSA
are functions of the package type, heatsink and the inter-
face between them. These values appear in heat sink data
sheets of heat sink manufacturers.
keep the die temperature below 150¡C.
In some cases, none of the packages will be sufficient to
dissipate the heat generated by the IC, and an external
heatsink will be required.
R
R
A heat sink effectively increases the surface area of the
package to improve the flow of heat away from the IC and
I
IN
I
OUT
V
IN
Smart
Regulator
V
OUT
Control
Features
}
I
Q
Figure 6. Single output regulator with key performance parameters
labeled.
into the surrounding air.
Application Diagram
BATTERY
V
OUT
V
IN
V
CC
C
1
C
2
CS8151
Microprocessor
WDI
I/O
______
RESET
______
RESET
C
Delay
Gnd
WAKE UP
C
Delay
I/O
7
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
